It is known that the friction loss between a piston ring and a piston largely accounts for that of the whole internal combustion engine. In recent years, decrease in the friction loss has been strongly demanded in order to increase the fuel efficiency of the internal combustion engine. Reducing the tension of the piston ring can be a way to reduce the friction of the piston ring. Reduction in the tension of the piston ring, however, conflicts with oil consumption of the internal combustion engine. Thus, it has been required to realize measures for reducing the oil consumption and reducing: the tension of the piston ring at the same time.
Known internal combustion engines such as a diesel engine include an anti-polish ring (also called a protect ring or a fire ring) attached to an uppermost portion of a cylinder liner. The anti-polish ring scrapes off combustion products (carbon) piled on a top land portion of the piston (an external periphery between a piston head and an uppermost ring groove). Thus, it is possible to prevent lopsided abrasion (carbon polish abrasion) due to the contact between the carbon and the cylinder liner, and the ascent of oil into a combustion chamber. Therefore, the oil consumption is reduced (refer to patent document 1).
In order to reduce oil consumption, Patent document 2 discloses a technology to prevent the oil from being scattered into the combustion chamber, in which the ring is provided above the piston head when the piston is in a top dead center to have the oil collide against the bottom face of the ring.
The anti-polish ring, on the other hand, is mainly applied to a large-displacement engine such as the diesel engine in many cases. In the diesel engine, the anti-polish ring is fitted into a step portion that is formed in an uppermost portion of the inner periphery of the cylinder liner. The cylinder liner is fixed inside a cylinder of a cylinder block by being latched on an upper side. Therefore, if the anti-polish ring is pressed and clamped together from upward by a cylinder head, the cylinder liner does not drop off downwardly.
Patent document 1: Japanese Unexamined Patent Application Publication No. Hei 11-294255
Patent document 2: Japanese Unexamined Patent Application Publication No. Hei 8-338301